References
- http://www.gghjournal.com/volume23/2/ab01.cfm
- http://www.sciencedirect.com/science?_ob=ArticleURL&_udi= B6WG5-4FS23JB-1&_user=7316560&_rdoc=1&_fmt=&_orig= search&_sort=d&view=c&_acct=C000050221&_version=1&_url Version=0&_userid=7316560&md5=b54894cd688df170493aaf7 b0b2c9979
- http://journals.cambridge.org/action/displayAbstract;jsessionid= 3BF70C0C5D703388827395431DCAB264.tomcat1?fromPage =online&aid=109463
- http://www.informaworld.com/smpp/content~content=a714028343 ~db=all